As described in my prior patent, U.S. Pat. No. 4,928,350, in certain hinge applications it is desirable for the hinge to allow the two objects it joins to be so close together when the hinge is at a certain position in its swing path that there is little or no gap between the objects. An example is a drop-leaf table. When the leaf and the table top are in the coplanar position—i.e., the leaf is extended—it is preferred that there be little or no gap between them.
Often in such drop-leaf table applications it is also preferred that no part of either hinge extend above the top and leaf when in the coplanar position—i.e., that the extended table top be smooth and uninterrupted, particularly uninterrupted by hinge pins that protrude above the surface. This requires that the hinge-pin axes be at an elevation below the upper surface of the table top. Normally that is not a problem if the leaf folds down. But if the leaf is to fold onto the top of the table, it is difficult to accomplish both objectives: positioning the hinge pins below the upper surface and having little or no gap between the top and the leaf when in the coplanar position. When using a conventional hinge, the greater the distance between the sunken hinge-pin axes and the upper surface of the table top, the wider must be the clearance gap between the top and the leaf.